Collaboration of Cerebello-Rubral and Cerebello-Striatal Loops in a Motor Preparation Task

International audienceIn this study, we used fMRI to identify brain regions associated with concentration (sustained attention) during a motor preparation task. In comparison with a non-concentration task, increased activities were observed (P < 0.05, FWEcorrected P values) in cerebellar lobules VI and VII, motor cortex, pre-supplementary motor area (pre-SMA), thalamus, red nucleus (RN), and caudate nucleus (CN). Moreover, analysis of effective connectivity inter-areal (psychophysiological interactions) showed that during preparation, concentration-related brain activity increase was dependent on Cerebellothalamo-pre-SMA-RN and Pre-SMA-CN-thalamo-M1 loops. We postulate that, while pre-SMA common to both loops is specifically involved in the movement preparation and readiness for voluntary movement through the striatum, the cerebellar lobule VI in conjunction with RN, likely through a cerebellar-rubro-olivary-cerebellar loop, might be implicated in concentration-related optimization of upcoming motor performances

The Click Test: A Novel Tool to Quantify the Age-Related Decline of Fast Motor Sequencing of the Thumb

International audienceAbstract : Background: The thumb plays a critical role for manual tasks during the activities of daily life and the incidence of neurological or musculoskeletal disorders affecting the voluntary movements of the thumb is high in the elderly. There is currently no tool to assess repetitive motor sequencing of the thumb during ageing.Objectives: To report a novel procedure (the Click Test) assessing the effects of ageing on fast motor sequencing of the thumb.Methods : Healthy subjects (n = 252; mean age +/- SD: 49.76 +/- 19.97 years; range: 19-89 years; F/M: 151/101) were asked to perform fast repeated flexion/extension movements of the thumb using a mechanical counter.Results: Motor performances (assessed by the number of clicks during 3 time periods: 15, 30 and 45 sec), significantly decreased as a function of age for both the dominant (age effect; p< 0.0001 for 15, 30 and 45 sec) and the non-dominant hand (p<0.0001 for 15, 30 and 45 sec). The number of clicks was significantly higher in males (gender effect; p<0.001) and was higher on the dominant side as compared to the non-dominant side (handedness effect: p<0.001). The Click Test is characterized by high repeatability (coefficients of variation from 3.20 to 4.47%), excellent intra-rater reliability (intra-class coefficients ICC ranging from 0.89 to 0.98), high inter-rater reproducibility (Pearson’s product correlation ranging from 0.85 to 0.96), high internal consistency (Cronbach alpha coefficient=0.95) and is highly correlated in terms of relative performances with the box and block test and the 9-hole peg test (positive linear correlation with the results of the box and block test: p<0.001 for 15, 30 and 45 sec for both the dominant and the non-dominant hand; negative linear correlation with the results of the 9-hole peg test: p<0.001 for 15, 30 and 45 sec for both the dominant and the non-dominant hand).Conclusion : The Click Test is an entirely novel and very low cost tool to reliably discriminate the ageing effects upon the performances during fast repetitive motor sequencing of the thumb. The potential clinical and research applications for motor functions are multiple, especially in acute and chronic neurological disorders affecting the thumb as well as in the field of rheumatology and orthopedics

Age-Related Differences in Functional and Structural Connectivity in the Spatial Navigation Brain Network

International audienceSpatial navigation involves multiple cognitive processes including multisensory integration, visuospatial coding, memory, and decision-making. These functions are mediated by the interplay of cerebral structures that can be broadly separated into a posterior network (subserving visual and spatial processing) and an anterior network (dedicated to memory and navigation planning). Within these networks, areas such as the hippocampus (HC) are known to be affected by aging and to be associated with cognitive decline and navigation impairments. However, age-related changes in brain connectivity within the spatial navigation network remain to be investigated. For this purpose, we performed a neuroimaging study combining functional and structural connectivity analyses between cerebral regions involved in spatial navigation. Nineteen young (μ = 27 years, σ = 4.3; 10 F) and 22 older (μ = 73 years, σ = 4.1; 10 F) participants were examined in this study. Our analyses focused on the parahippocampal place area (PPA), the retrosplenial cortex (RSC), the occipital place area (OPA), and the projections into the visual cortex of central and peripheral visual fields, delineated from independent functional localizers. In addition, we segmented the HC and the medial prefrontal cortex (mPFC) from anatomical images. Our results show an age-related decrease in functional connectivity between low-visual areas and the HC, associated with an increase in functional connectivity between OPA and PPA in older participants compared to young subjects. Concerning the structural connectivity, we found age-related differences in white matter integrity within the navigation brain network, with the exception of the OPA. The OPA is known to be involved in egocentric navigation, as opposed to allocentric strategies which are more related to the hippocampal region. The increase in functional connectivity between the OPA and PPA may thus reflect a compensatory mechanism for the age-related alterations around the HC, favoring the use of the preserved structural network mediating egocentric navigation. Overall, these findings on age-related differences of functional and structural connectivity may help to elucidate the cerebral bases of spatial navigation deficits in healthy and pathological aging

Recombination and large structural variations shape interspecific edible bananas genomes

Admixture and polyploidization are major recognized eukaryotic genome evolutionary processes. Their impacts on genome dynamics vary among systems and are still partially deciphered. Many banana cultivars are triploid (sometimes diploid) interspecific hybrids between Musa acuminata (A genome) and M. balbisiana (B genome). They have no or very low fertility, are vegetatively propagated and have been classified as 'AB', 'AAB' or 'ABB' based on morphological characters. We used NGS sequence data to characterize the A vs. B chromosome composition of nine diploid and triploid interspecific cultivars, to compare the chromosome structures of A and B genomes and analyze A/B chromosome segregations in a polyploid context. We showed that interspecific recombination occurred frequently between A and B chromosomes. We identified two large structural variations between A and B genomes, a reciprocal translocation and an inversion that locally affected recombination and led to segregation distortion and aneuploidy in a triploid progeny. Interspecific recombination and large structural variations explained the mosaic genomes observed in edible bananas. The unprecedented resolution in deciphering their genome structure allowed us to start revisiting the origins of banana cultivars and provided new information to gain insight into the impact of interspecificity on genome evolution. It will also facilitate much more effective assessment of breeding strategies

Consensus Paper: The Role of the Cerebellum in Perceptual Processes

Various lines of evidence accumulated over the past 30 years indicate that the cerebellum, long recognized as essential for motor control, also has considerable influence on perceptual processes. In this paper, we bring together experts from psychology and neuroscience, with the aim of providing a succinct but comprehensive overview of key findings related to the involvement of the cerebellum in sensory perception. The contributions cover such topics as anatomical and functional connectivity, evolutionary and comparative perspectives, visual and auditory processing, biological motion perception, nociception, self-motion, timing, predictive processing, and perceptual sequencing. While no single explanation has yet emerged concerning the role of the cerebellum in perceptual processes, this consensus paper summarizes the impressive empirical evidence on this problem and highlights diversities as well as commonalities between existing hypotheses. In addition to work with healthy individuals and patients with cerebellar disorders, it is also apparent that several neurological conditions in which perceptual disturbances occur, including autism and schizophrenia, are associated with cerebellar pathology. A better understanding of the involvement of the cerebellum in perceptual processes will thus likely be important for identifying and treating perceptual deficits that may at present go unnoticed and untreated. This paper provides a useful framework for further debate and empirical investigations into the influence of the cerebellum on sensory perception

Consensus Paper: Radiological Biomarkers of Cerebellar Diseases

Hereditary and sporadic cerebellar ataxias represent a vast and still growing group of diseases whose diagnosis and differentiation cannot only rely on clinical evaluation. Brain imaging including magnetic resonance (MR) and nuclear medicine techniques allows for characterization of structural and functional abnormalities underlying symptomatic ataxias. These methods thus constitute a potential source of radiological biomarkers, which could be used to identify these diseases and differentiate subgroups of them, and to assess their severity and their evolution. Such biomarkers mainly comprise qualitative and quantitative data obtained from MR including proton spectroscopy, diffusion imaging, tractography, voxel-based morphometry, functional imaging during task execution or in a resting state, and from SPETC and PET with several radiotracers. In the current article, we aim to illustrate briefly some applications of these neuroimaging tools to evaluation of cerebellar disorders such as inherited cerebellar ataxia, fetal developmental malformations, and immune-mediated cerebellar diseases and of neurodegenerative or early-developing diseases, such as dementia and autism in which cerebellar involvement is an emerging feature. Although these radiological biomarkers appear promising and helpful to better understand ataxia-related anatomical and physiological impairments, to date, very few of them have turned out to be specific for a given ataxia with atrophy of the cerebellar system being the main and the most usual alteration being observed. Consequently, much remains to be done to establish sensitivity, specificity, and reproducibility of available MR and nuclear medicine features as diagnostic, progression and surrogate biomarkers in clinical routine